1. Field of the Invention
The invention relates to a control device and control method for a vehicular induction motor, and in particular to a control device and control method for a vehicular induction motor, which controls the induction motor that drives the vehicle so as to prevent overheating of an inverter that controls supply of electric current to the induction motor when the inverter is locked.
2. Description of Related Art
Electric vehicles or hybrid vehicles that run with power of electric motors are known. In this type of vehicle, when the motor rotates during normal running of the vehicle, alternating current flows through each of switching devices of an inverter that controls supply of current to the motor. However, when the motor is brought into a locked state, large direct current flows through only a particular switching device or devices of the inverter, and the temperature of the switching device(s) is elevated.
In Japanese Patent Application Publication No. 2010-130890 (JP 2010-130890 A), a technology of controlling a motor so as to reduce torque of the motor when the motor is brought into a locked state is disclosed. With this control, the vehicle moves backward, and the motor rotates, so that current is prevented from being concentrated in a particular phase, and the temperature of a particular switching device(s) of the inverter is less likely or unlikely to be elevated to a high level.
In Japanese Patent Application Publication No. 2012-228131 (JP 2012-228131 A), a technology of curbing increase of the temperature of a particular phase when a motor is in a locked state, by calculating an allowable lock time for which no problem occurs even in the locked state, based on a coil temperature of the motor, and passing current through phases other than the particular phase that is being heated, when the allowable lock time passes, is described.